Furnace



June 23, 1959 McNEAL 2,891,520

' FURNACE Filed April 11, 1955 I Y .5 Sheets-Sheet 1 United States Patent FURNACE Raymond E. McNeal, Chicago, 111., assignor to Chicago Down Draft Furnace Co.,' Chicago, 111., a corporation of Illinois 7 7 Application April 11,. 1-955, Serial No. 500,374

4 Claims. c1. 1z2-94 Thev present invention relates. to furnace construction and particularly to theadaptationof steam boilers to efficient use with. rotaryand gun type fuel burners of the modern type.

The use of furnace extensions applied to boilers for purposes of utilizinggun type fuel burners is, of course, generally known and was described in my earlier Patent No. 1,910,349., issued May 23, 1933. Experience with the burner extensions of the cylindrical, completely insulated. type of furnace extension described in the above mentioned earlier. patent has proved. the general efficiency of such a system. However, when rotary type burners are utilized with the cylindrical type furnace extension there shown, several important difficulties became apparent and the efficiency of operation, both from the point of view of maintenance and fuelcombustion; was noticeably poor. While such deficiencies occur only with the, rotary type burner and certain. other types of modern fuel burner equipment, nevertheless it was found that fulfnace extensions of the-type illustrated in my earlier patent were limited, for efiicient use,.to only' a few types of fuel burners. The furnace extension of thepresent invention is, on the other hand, constructed andarranged to permit its efiicient operationv withsubstantially any type, of commercial fuel burnernow-known and marketed.

In addition to the difiiculty of providing a-furnace extension capable of efiicient operation with all types of burners, several additional problems of substantial importance must be solved before an optimum furnace constnictionis achieved. These problems have proved particularly troublesome because inherently improvement relative to one aspect, of furnace construction is atthe expense of a decrease of efliciency relative to another. For example, it is desirable, in constructing furnace extensionsof the general type illustratedin my earlier patent, to provide maximum transfer in the furnace. extension to. the boiler feed 'Water heating tubes surrounding the combustion chamber. Achievement of such efliciency would suggest the elimination of all firebrick .and other similar insulating materials from around the-water tubes. However, it is also desirable to provide complete combustion and it has been found that impingement of the flame upon water cooled, pipes tends to retard combustion of thefuel therealong, thereby providing incomplete combustion and inefficient operation. Further, problems of proper fuel turbulence, and, furnace hot spots are present.

In accordance with the principles of the, present invention, the problfims. above indicated. have been satisfactorily solved and at the same time, atfurnace extension capable of use with substantially any type of existing fuel burning equipment has beenachieved. According to the principles of the present invention an extension combustion chamber is provided for attachmentto. a boiler in a manner somewhat similar to that illustrated in my earlier patent. However, the extension is, substantially difierent in shape. In accordance with the present invention, the extension is of diverging-converging or, in other "ice words, barrel shape. A fuel burner of either the rotary or gun type is positioned at the end of the barrel remote from the boiler and fuel is injected into the extension where initial burning takes place. In accordance with the present invention, water tubes may extendaxially of the furnace extension and be longitudinally bowed to form the diverging-convergingshape or, in a modified arrangement, may be arranged in a series 'of circular loops having progressively increasing and subsequently decreasing diameters.

As a result of the initial divergence of the combustion chamber walls, fuel sprayed in a fan-like manner by rotary burners does not impinge on the water cooled tubes tthereby permitting the use of uncovered tubes for better heat transfer from the burning fuel to the water. At the same time, the provision of firebrick closely behind the tubes, coupled with the increased spacing between tubes at the midportion of the extension assures ignition in the furnace extension and provides proper combustion without leaving any unburned fuelresidues on the chamber walls. Further, by providing the converging exit portion of the furnace extension, the burning gases are forced, in a venturi-like manner, to change directions and accelerate during their passage into the main boiler. This action causes a substantial turbulence and improved secondary ignition in the furnace proper thereby insuring complete fuel combustion. In addition, the converging shape of the furnace extension eliminates completely any dead air spaces in the furnace extension immediately' adjacent the boiler entrance, which dead air spaces have in the past; been caused'by'the tendencyv of air to assume streamlined flow from the combustion chamber into the boiler through the relatively small'diameter boiler inlet, thus pocketing gases adjacent the front wall of the boiler radiallyoutwardly of the boiler inlet opening.

It is therefore an object of the present invention to provide an improved furnaceextension and return water heater for boilers.

Another object of the present invention is to provide a furnace extension capable of extremely eflicientfiuse with rotary as well as gun type burners. .1;

Still a further object of the'present invention isiito provide a furnace extension for use with gun and-rotary type fuel burners and which provides at least a portion of the walls thereof with uncovered water pipes.

Yet a further object of the present invention is to pro.- vide an extension type preliminary combustion chamber having a venturi-like exit to a further combustion chamber whereby combustion gases are burned completely.

Another object of the invention is to provide a novel diverging-converging combustion chamber for use with rotary type fuel burners.

'A feature of the invention is the provision of Water pipes extending generally longitudinally of the furnace extension and defining a diverging-converging peripheral surface.

Another feature of the invention is the provision of a diverging-converging combustion chamber having water pipes at the outer periphery thereof wherein the said water pipes are positioned out of line with the burning fuel.

Still other and further objects and features of the present invention will at once become apparent to those skilled in the art from a considerationof the attached drawings wherein the apparatus. of the present invention is shown installed in two common types of boiler installations and, wherein:

Figure 1 is a fragmental sectional view ofafire'tube boiler showing an extension. furnace constructedaccording to the present invention applied thereto;

Figure 2 is a cross-sectional view taken along the line II-II of Figure 1;

Figure 3 is a fragmental sectional view through a boiler of Scotch type showing an oil burner extension furnace constructed according to the present invention applied thereto;

Figure 4 is a fragmental sectional view, in elevation, of a boiler utilizing a modified form of the invention; and

Figure 5 is a cross sectional view taken along line VV of Figure 4.

As shown on the drawings:

In the installation shown in Figure l, a fire tube boiler of generally conventional design is supported on the usual masonry setting indicated generally at 11. The boiler 10 is provided with a combustion chamber 12 to which are connected a plurality of conventional fire tubes 13. The tubes 13 are secured to the header wall 14 of the chamber in a conventional manner, such as, for example, by rolling over the ends thereof. The area surrounding the fire tubes 13, indicated at 15 is filled With water to be heated by heat transfer relationship with the tubes 13 and the walls of chamber 12.

As may be seen, the boiler 10 is mounted on a conventional ceramic foundation and is provided with a furnace extension secured to the main boiler inlet opening 21 by bolts or other conventional securing means at the outlet header 22. The extension 20 is supported on foundation elements 23 and 24 and is provided with a conventional fuel burner 25 which is illustrated in a somewhat diagrammatic form and which may be of substantially any known type capable of projecting fuel and air into the chamber 26 of the extension 20.

Unlike prior art structures such as, for example, that shown in my above identified prior patent, the furnace extension 20 of the present invention is non-cylindrical. As may be seen from a consideration of Figure 1, the inlet header 27, which may be connected to a water return pipe 28 leading to the boiler header 14, or, alternatively, to a separate header, is connected to the outlet header 22 by means of a plurality of bowed heat transfer tubes 29. The tubes 29 are preferably backed by a steel shell 30 provided with a section of insulation 31 on the inner surface of the shell between the shell and the tubes. Additionally, if desired, insulation may be provided completely around the tube 29 immediately adjacent the extension inlet and the burner 25 to thereby provide a hot spot assuring positive ignition under all conditions of operation.

As a result of the above construction, fuel injected into the chamber 26 burns substantially in the enlarged area of the furnace extension without impingement on the diverging tube walls. This combustion is, of course, accompanied by expansion of the resultant gases and as a result of the necked down or venturi eifect provided by the convergence of the tubes 29 and the firebrick insulation 32, the burning gases are introduced into the chamber 12 at high velocity. This high velocity movement of the gases, with subsequent room for expansion in the chamber 12 causes turbulence which, it has been found, provides substantially complete burning of all the combustible elements in the fuel, thereby eliminating smoke conditions and providing maximum operating efficiency.

Where it is desired to utilize the rotary type burner, the diverging-converging construction of the furnace extension 20 provides substantially improved performance. As has been indicated above, the fuel injected by a rotary type burner will enter the chamber 26 in a fan, or conical, pattern. Since the tubes 29 are relatively cool from the water flowing therethrough, fuel impinging on the outer surfaces thereof would tend to accumulate there Without burning. Accordingly, by providing a diverging section of the furnace extension immediately downstream of the burner, the conical fuel pattern of the rotary type burner conforms generally to the internal configuration of the chamber 26 and a minimum of the fuel is permitted to strike any uncovered tubes. As a result, the tubes are positioned in immediate proximity to the burning fuel without being touched'by it, thereby providing a maximum of heat transfer with a minimum of interference with the burning of the fuel. In addition to the fact that the divergence of the furnace tubes minimizes fueltube contact, the divergence also provides for separation of the boiler tubes 29 at the point of maximum divergence. This increases the area of firebrick exposed whereby any fuel impinging on the extension wall at the point of initial convergence will mainly strike hot firebrick and be ignited instantly. Fuel impinging on the hot surface of the firebrick 31 immediately ignites and as a result substantially no fuel goes unburned to form carbon sludge or the like in the furnace. It will be understood, therefore, that the uncovered portions of the tube 29 accept heat at high efliciency from the burning gases, through radiation as well as conduction, and at the same time the relatively low temperature of the tubes 29 in no way adversely alfects the necessary combustion. This results in an unusually efiicient burner arrangement capable of providing excellent heating results.

It has been found, in addition to the features above discussed, that provision of a diverging-converging burner chamber eliminates dead air spaces commonly found in prior art structures at the corners indicated at 33 and 34. In the cylindrical type furnace extensions the burning fuel firms eddy currents in these areas which move relatively slowly and which, it has been found, cause firebrick ordinarily used at those points to deteriorate at an extremely rapid rate. By providing the converging structure adjacent the exit from the furnace extension so such pockets are formed and accordingly it has been found that the firebrick 31 has an unexpectedly long life and, further, that the tubes 29 likewise are not adversely affected at the ends thereof immediately adjacent the inlet header 27.

It will, of course, be apparent from a consideration of Figure 1 that the burner extension 20 is inclined from the horizontal at a slight angle in the upward direction. This angle will, of course, vary. depending upon the construction of the main burner combustion chamber 12 and the type of boiler to which the extension is to be attached. For example, the inclination is shown in reverse in the embodiment shown in Figure 3 wherein a boiler of the Scotch type is illustrated. As is shown, the extension 20a is inclined downwardly toward the furnace and opens into the corrugated boiler firebox 12a which is in turn surrounded by water within the main boiler section 15a. In view of the reverse inclination of the furnace extension 20a, the water inlet 28a enters the inlet header 27a which is positioned at the downstream end of the furnace extension and leaves the outlet header 22a positioned at the inlet end of the extension 20a, through the conduit 35. The tubes 29b are substantially identical to the tubes 29 and the firebrick arrangement 32a, shell 30a and insulation section 31a are likewise substantially identical in construction and function as those of the embodiment shown in Figure 1. As a result of the reverse inclination, the water enters at the bottom of the furnace extension and flows upwardly toward the uppermost point thereof by thermal action thereby eliminating the need for pumps. However, it will be understood that by means of forced circulation the flow could be reversed if desired.

An advantage obtainable through the downward inclination of the furnace may be understood when it is remembered that the force of gravity on the fuel will cause the cone of fuel generated by a rotary burner to droop slightly. This causes the uppermost surface of the cone to assume a rather horizontal position and the lowermost surface of the cone to drop off sharply, thus even more nearly conforming the conical shape of the fuel pattern to the actual internal walls of the combustionchamher and assuring that a minimum amount of fuel impinges on the uncovered, cool, portions of the conduits 29b.

As in the case of the embodiment shown in Figure 1 the furnace extension and boiler illustrated in Figure 3 are mounted in conventional masonry foundations.

The diverging-converging furnace extension may be provided with transversely mounted circular tubes instead of the longitudinally extending bent tubes shown in Figures 1 through 3. Such a modified form is illustrated in Figures 4 and 5.

As shown in Figure 4 a furnace extension generally indicated at 200 is positioned adjacent the entrance 220 in a Scotch marine type of boiler generally indicated at 100 and having a water space 150 and a corrugated combustion chamber or firebox 120. As in the modifications illustrated in Figures 1 through 3, also, the furnace extension 200 is provided with a steel outer shell 300 supported by columnar supports 230 and 240. It will be noted that the shell 300 takes the divergent-convergent form previously discussed and is lined with a firebrick lining 310 positioned immediately behind a plurality of circular tubes 290.

The circular or annular tubes 290 are each connected to respective inlet and outlet headers 280 and 350 by risers 281 and 351 respectively. If it is found desirable, the header 280 may be supported by an additional masonry support 282 as well as the main front bulkhead 283 of the furnace 100.

In operation the furnace extension illustrated in Figures 4 and 5 is fundamentally similar to those shown in Figures 1 through 3. Fuel injected by the burner 250 expands and burns as it passes through the diverging portion of the extension 200. It is then constricted by the converging portion of the extension and passes through the opening 220 into the main boiler chamber 120 at substantially increased velocity providing highly efficient, complete, combustion to take place before the fuel products leave the chamber 120. As will be noted from Figure 5, substantially no corner dead air pockets are provided between the extension 200 and the opening 220 and accordingly the useful life of the firebrick liner 310 as well as the tubes 290 themselves is materially increased.

As will be noted, due to the fact that each individual tube 290 feeds directly from a lower header 280 to an upper header 350, the furnace extension 250 need not be inclined as shown in Figures 1 and 3. Thus, the extension 210 is substantially horizontally positioned, thereby permitting the use of the extension with furnaces having relatively low doors 220. In this respect, it will be understood that the header 280 may be positioned closer to the shell 300 than illustrated in Figure 4 if necessary to permit use of the extension 200 with a low furnace opening and it will also, of course, be understood that the headers 280 and 350 may, themselves, be slightly inclined to the horizontal if so desired. In such a case it is preferred that the header 280 be inclined upwardly as it extends to the left of the main bulkhead 283 shown in Figure 4 and that the header 350 be inclined upwardly as it approaches the bulkhead 283 shown in the same figure.

It will thus be seen that I have provided a novel and substantially improved furnace extension for use with modern gun and rotary type fuel burners and which is capable of providing extremely efiicient transfer of heat to the water jacket surrounding the extension and at the same time providing for complete combustion of all fuel.

It will, of course, be understood that the furnace extension of the present invention may be used with any conventional boiler in the same manner as illustrated in connection with the fire tube and Scotch type illustrated. For example, the present apparatus is admirably suited to water tube boilers of all types.

Since it will be understood that many further modifications and variations may be made in the above structure without departing from the scope of the novel concepts thereof, it is intended that the instant invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. In combination with a. boiler having a water space, a firebox and a firebox inlet opening of reduced diameter, a furnace extension. having an outlet substantially the same dimension as. said firebox inlet and secured generally horizontally in juxtaposition thereto, an inlet to said furnace extension through which fuel is introduced, burner means in said inlet introducing fuel generally axially into the furnace extension in a diverging conical spray, a diverging interior surface in said extension substantially conforming to and extending generally parallel to the outer surface of the diverging conical spray as it extends toward said extension outlet and extending to a point of maximum diameter substantially greater than the diameter of said outlet prior to which point substantial ignition occurs without fuel impingement on said interior surface and from thence converging to said extension outlet, whereby said extension outlet and said firebox inlet form a restriction during fuel combustion creating turbulence during fuel combustion, said extension having a refractory interior lining surface and a plurality of water carrying heat transfer tubes positioned immediately adjacent said refractory lining surface and uncovered thereby for exposure to the burning fuel in said extension, said tubes being substantially spaced from each other in the area of maximum diameter and convergence of said extension, thereby providing water tubes generally conforming to the diverging-converging nature of the fuel flow pattern and of the said interior surface but separated by substantial areas of refractory to assure efficient ignition of any fuel impinging on the interior surface of said extension, and means connecting said water tubes to said water space, each of said tubes having its outlet at a point substantially higher than its inlet to provide thermal circulation in said tubes and in said Water space.

2. A furnace extension and boiler construction in accordance with claim 1 wherein each of said water carrying heat transfer tubes comprises a circular tube lying in a generally vertical plane and said last-named means comprises separate outlet and inlet generally longitudinally extending headers connected to said water space at vertically spaced points and to each circular tube at the extreme top and bottom thereof respectively.

3. A furnace extension and boiler construction in accordance with claim 1 wherein each of said water carrying heat transfer tubes comprises a circular tube lying in a generally vertical plane and said last-named means comprises separate outlet and inlet longitudinally extending headers positioned completely outside of said furnace extension and connected to said water space at vertically spaced points and connected to each of said circular tubes at the extreme top and bottom thereof respectively by a generally vertically extending tube passing through the respective upper and lower portions of the interior surface of said extension.

4. A furnace extension and boiler construction in accordance with claim 1 wherein each of said water carrying heat transfer tubes comprises a generally longitudinally extending tube bent along its length to conform to said interior surface and said last named means comprises separate generally circular outlet and inlet headers at opposite ends of said furnace extension and connected respectively to said water space at points above and below the uppermost and lowermost points of said extension.

References Cited in the file of this patent UNITED STATES PATENTS 443,770 Keiper Dec. 30, 1890 475,715 Wegener May 24, 1892 (Other references on following page) 7 UNITED STATES PATENTS McNeal May 23, 1933 Coutant July 25, 1933 LaMont Aug. 28, 1934 Echo Dec. 31, 1940 Cook Dec. 7, 1943 Crotty Oct. 16, 1945 Olson *et a1. Jan. 11, 1955 FOREIGN PATENTS Great Britain Mar. 18, 1953 

